The Smithsonian Astophysical Observatory/NASA Astrophysics Data System (ADS) is 20 years old this spring. It is operated by SAO under a NASA grant.
In 1993, the ADS Astract Service launched online with 160K of records for 200 users; 20 years later there are 57 million citations for over 10 million users.
Today, the ADS is a digital library portal for astronomical research in three bibliographic databases: Astronomy & Astrophysics, Physics and arXiv e-prints. The ADS provides access to citations, full-text scans, with links to data catalogs and archives. This central discovery engine is used everyday by millions.